I am currently working on the modeling of the distribution of different vegetation types and associate species in eastern Africa. In absence of more detailed climate data for the region, a great source of global climatic data is the WorldClim website. Besides the usual monthly temperature and rainfall data, it provides bioclimatic variables which are derived from these monthly temperature and rainfall values in order to generate more biologically meaningful variables. However, it only does this for the current conditions (interpolations of observed data, representative of 1950-2000) but not yet (?) for the future conditions (downscaled data from global climate model (GCM) output, IPPC 3rd assessment). Thus, I had to calculate them myself, which I did using GRASS GIS and R.
For ArcInfo there is an aml script available on the WorldClim site. However, I do most of my GIS work in GRASS GIS in Linux so I decided to write a script for GRASS. I am not a programmer and if I have to do some scripting I normally would use R. However, because GRASS runs directly from the command line I though it might actually be easier to write a batch script. Wrong idea as it turned out, primarily because I know next to nothing about the command line syntax. Still, I managed at the end to come up with something which can be used to calculate the bioclimatic data from GRASS GIS. If you are interested, you can download the script from here. To run the script you’ll need to make it executable:
> cd path_to_folder_where_you_saved_the_script
> chmod a+x r.bioclim
I might rewrite it later to open a GUI when run, but for now you’ll have to change a few lines in the script before running it. It assumes you have a mapset with monthly rainfall, minimum and maximum temperatures. You will need to give the name of the mapset (Inmap on line 62) and the names of the variables (Tmax, Tmin and Prec on line 63-65). The script will create a new mapset (you’ll need to give a name on line 61) and will generate 19 bioclim variables (see script for more details) in that mapset. Open GRASS GIS and run the following on the command line:
> cd path_to_folder_where_you_have_the_script
I don’t know if the same script runs under GRASS on Windows, but you probably will need to make some adaptations. And to end with the usual disclaimer, if you decide to try it out, you’ll run in entirely on your own risk.
Update: there is also the R package dismo that lets you calculate the bioclimate data. Note that this will be done in R, so very large grids may pose a problem.